Gem

ABSTRACT

A gem having a faceted crown which is inclined with respect to the main axis and which is defined on the one hand by a preferably flat table and on the other hand by a peripheral edge of the gem, and a faceted pavilion which is inclined with respect to the main axis and which adjoins the peripheral edge and which converges to a tip, wherein the facets ( 3 ) of the crown ( 2 ) are all inclined at the same crown angle (β) with respect to the main axis ( 1 ), while the facets ( 7, 7 ′) of the pavilion ( 6 ) are inclined at two different pavilion angles (α 1 , α 2 ) with respect to the main axis ( 1 ), wherein the facets ( 7 ) of the pavilion ( 6 ) which are inclined at a first pavilion angle (α 1 ) extend to the peripheral edge ( 5 ) and the facets ( 7′ ) of the pavilion ( 6 ) which are inclined at a second pavilion angle (60  2 ) start from the tip ( 8 ) without reaching the peripheral edge ( 5 ).

[0001] The invention concerns a gem having a faceted crown which isinclined with respect to the main axis and which is defined on the onehand by a preferably flat table and on the other hand by a peripheraledge of the gem, and a faceted pavilion which is inclined with respectto the main axis and which adjoins the peripheral edge and whichconverges to a tip.

[0002] In the case of artificial gems, in particular of glass, there isfrom time to time an interest in achieving a reflection characteristicwhich radiates in as wide-spread a fashion as possible, when there iscentral illumination on to the table.

[0003] In order to achieve that, the invention proposes that the facetsof the crown are all inclined at the same crown angle with respect tothe main axis while the facets of the pavilion are inclined at twodifferent pavilions angles with respect to the main axis, wherein thefacets of the pavilion which are inclined at a first pavilion angleextend to the peripheral edge and the facets of the pavilion which areinclined at a second pavilion angle start from the tip without reachingthe peripheral edge.

[0004] The applicants' measurements have shown that a widening of thereflection characteristics can be achieved by cutting a second pavilionangle, that is to say a second layer of facets, which are inclined at ashallower angle with respect to the main axis. Upon central illuminationin the direction of the main axis on to the table therefore relevantlevels of radiation intensity are still to be expected even atrelatively large angles with respect to the main axis.

[0005] It has proven to be particularly advantageous if the facets ofthe pavilion which are inclined at the second pavilion angle, in a viewfrom below directed on to the tip of the gem, extend radially over adistance of between 25% and 75% of the projected tip-peripheral edgespacing (grinding depth of the second layer of between 25% and 75%).

[0006] A further alternative configuration of the invention ischaracterised in that the facets of the crown are all inclined at thesame crown angle with respect to the main axis while the facets of thepavilion are inclined at two different pavilion angles with respect tothe main axis, wherein the facets of the pavilion which are inclined ata first pavilion angle extend to the peripheral edge and the facets ofthe pavilion which are inclined at a second pavilion angle start fromthe tip, wherein the crown angle is between 40° and 44°, preferablyabout 42°, the first pavilion angle is between 40° and 44°, preferablyabout 42°, and the second pavilion angle is between 32° and 36°,preferably about 34°.

[0007] Further advantages and details of the invention are described ingreater detail with reference to the specific description hereinafter.

[0008]FIGS. 1a, 1 b and 1 c show a 12-facet gem (chaton) in accordancewith the state of the art, which has a single-layer crown and asingle-layer pavilion,

[0009]FIGS. 2a, 2 b and 2 c show an embodiment of a gem (chaton)according to the invention, having a second pavilion layer with a 50%grinding depth,

[0010]FIGS. 3a, 3 b and 3 c show a further embodiment of a gem accordingto the invention with a second pavilion layer with a grinding depth of75%,

[0011]FIG. 4 shows measurement of the height angle theta,

[0012]FIG. 5 shows measurement of the width angle phi,

[0013]FIGS. 6, 7 and 8 each show diagrammatic representations of thereflected light strength in dependence on the height angle theta with aconstant angle phi=0, wherein FIG. 6 concerns a gem according to thestate of the art as shown in Figures 1 a, 1 b and 1 c, FIG. 7 shows agem according to the invention as shown in FIGS. 2a, 2 b and 2 c andFIG. 8 concerns a gem according to the invention as shown in FIGS. 3a, 3b and 3 c.

[0014] The gems illustrated in the Figures are of the type of aso-called chaton.

[0015] The 12-facet chaton shown in Figures 1 a, 1 b and 1 c has a crown2 with twelve facets 3, which is inclined with respect to the main axis1 and which is delimited by a flat table 4. Adjoining the peripheraledge 5 which can also be in the form of a girdle bevelled parallel tothe main axis 1 is the pavilion 6 which also has twelve facets 7 whichconverge to a tip 8. The crown angle is denoted by β and the pavilionangle by α.

[0016] A 12-facet chaton as shown in Figures 1 a, 1 b and 1 c gives, fora width angle phi 0 in dependence on the height angle theta a reflectioncharacteristic as is shown approximately in FIG. 6.

[0017] An increase in the width of that reflection characteristic, thatis to say relevant levels of light intensity with greater angles theta,can be achieved if, in accordance with the invention, there is ground infrom the tip 8 a second layer of facets with a second pavilion angle, asis shown by FIGS. 2a, 2 b, 2 c and 3 a, 3 b and 3 c. The crown 2 of thegem according to the invention is in that respect of the sameconfiguration as in the state of the art, that is to say of asingle-layer configuration with a single crown angle β of the facets 3with respect to the main axis 1.

[0018] Now, in accordance with the invention, on the pavilion 6, thereare twelve facets 7 which are inclined at the pavilion angle α₁ withrespect to the main axis 1. In addition there are twelve further facets7′ which are inclined at a second shallower pavilion angle α₂ withrespect to the main axis 1 and which are ground in from the tip 8 butwithout reaching the peripheral edge 5.

[0019] In the embodiment shown in FIGS. 2a, 2 b and 2 c the facets 7′,in the view from below directed on to the tip 8 of the gem, as in FIG.2c, extend radially outwardly over a distance of 50% of the projectedtipperipheral edge spacing. Reference is made here to a grinding depthof the second layer of 50%.

[0020] Such a gem in accordance with the invention, as shown in FIGS.2a, 2 b and 2 c, affords a reflection characteristic as is shownapproximately in FIG. 7. In comparison with FIG. 6, there are lightcomponents with greater theta angles, that is to say a distribution oflight which radiates more widely.

[0021]FIGS. 3a, 3 b and 3 c show an embodiment of a gem according to theinvention with a grinding depth of 75%. That affords the lightdistribution approximately as shown in FIG. 8.

[0022] In accordance with a variant of the invention there is provided agem in which the crown angle β is between 40° and 44°, preferably beingabout 42°. The first pavilion angle α₁ is desirably between 40° and 44°,preferably being about 42°, while the second pavilion angle α₂ isbetween 32° and 36°, preferably being about 34°. With those angles,particularly in the case of a gem of ground glass with a refractiveindex of between 1.50 and 1.65, the reflection characteristic is goodand radiates widely.

[0023] It will be appreciated that the invention is not limited to theembodiments illustrated by way of example, for example the number offacets may differ. Even numbers of facets 8, 12 or 16 have proven to bepreferable. In principle however other numbers of facets, in particularodd numbers of facets, are certainly conceivable and possible. Thenumber of facets of the crown on the one hand and the pavilion on theother hand also do not necessarily have to be the same, although anidentical number of facets in the crown of the first pavilion angle andthe second pavilion angle has been found to be advantageous.

1. A gem having a faceted crown which is inclined with respect to themain axis and which is defined on the one hand by a preferably flattable and on the other hand by a peripheral edge of the gem, and afaceted pavilion which is inclined with respect to the main axis andwhich adjoins the peripheral edge and which converges to a tip,characterised in that the facets of the crown are all inclined at thesame crown angle (β) with respect to the main axis, while the facets ofthe pavilion are inclined at two different pavilion angles (α₁, α₂) withrespect to the main axis, wherein the facets of the pavilion which areinclined at a first pavilion angle (α₁) extend to the peripheral edgeand the facets of the pavilion which are inclined at a second pavilionangle (α₂) start from the tip without reaching the peripheral edge.
 2. Agem as set forth in claim 1, characterised in that the number of facetsof the crown, the number of facets at the first pavilion angle (α₁) andthe number of facets at the second pavilion angle (α₂) are the same andpreferably 8, 12 or
 16. 3. A gem as set forth in claim 1, characterisedin that the facets of the pavilion which are inclined at the secondpavilion angle (α₂), in a view from below directed on to the tip of thegem, extend radially over a distance of between 25% and 75% of theprojected tip-peripheral edge spacing.
 4. A gem as set forth in claim 1,characterised in that it comprises ground glass.
 5. A gem as set forthin claim 4, characterised in that the refractive index of the glass isbetween 1.50 and 1.65.
 6. A gem having a faceted crown which is inclinedwith respect to the main axis and which is defined on the one hand by apreferably flat table and on the other hand by a peripheral edge of thegem, and a faceted pavilion which is inclined with respect to the mainaxis and which adjoins the peripheral edge and which converges to a tip,characterised in that the facets of the crown are all inclined at thesame crown angle (β) with respect to the main axis, while the facets ofthe pavilion are inclined at two different pavilion angles (α₁, α₂) withrespect to the main axis, wherein the facets of the pavilion which areinclined at a first pavilion angle (α₁) extend to the peripheral edgeand the facets of the pavilion which are inclined at a second pavilionangle (α₂) start from the tip, wherein the crown angle (β) is between40° and 44°, preferably about 42°, the first pavilion angle (α₁) isbetween 40° and 44°, preferably about 42°, and the second pavilion angle(α₂) is between 32° and 36°, preferably about 34°.